Currently, mobile communication networks are primarily Circuit-Switched (CS) domain networks, including Global System for Mobile communication (GSM) and Code Division Multiple Access (CDMA). Service providers set up good and diversified service platforms based on CS domain networks. In such platforms, a Mobile Switching Center (MSC) is responsible for routing calls and executing service logics, for example, Call Forwarding (CF) service. In addition, the MSC works together with other Application Servers (ASs) such as a Color Ring Back Tone (CRBT) server in the CS domain network to provide services. However, the service provision of the CS domain network requires support of the visited MSC, which is unfavorable to introducing new services.
The Internet protocol Multimedia Subsystem (IMS) is an effective solution to emergence of multiple networks (for example, mobile network, fixed network, television network) in the communication field currently. In the evolution process of the IMS network, it is necessary to ensure consistent service experience of the user regardless of the access mode such as CS network access and Packet Switched (PS) network access. The user does not need to perceive the specific access mode, for example, in receiving or sending a call and adding or invoking service data configuration. Therefore, the 3rd Generation Partnership Project (3GPP) puts forward IMS Centralized Service (ICS), in which the CS network bears voice or Visual Phone (VP) media to set up an IMS call on a User Equipment (UE), and the AS in the IMS provides services for the call. An important aspect of the ICS is that the traditional CS UE accesses an IMS network. When the CS UE accesses the IMS network, the MSC server is an enhancement of the MSC server of the existing CS network. The enhanced MSC server can convert the CS domain signaling (3GPP TS 24.008) into a Session Initial Protocol (SIP) signaling, and send the SIP signaling to the IMS network so that the user can enjoy the IMS service. Under the control of the MSC server, a Media Gateway (MGW) performs switching between the CS access bearing and the Real-time Transport Protocol (RTP) bearing. RTP bearing means that the media stream is transmitted over an RTP. The RTP runs on an IP network. The MSC server may control one or more MGWs. The MSC server and the MGW controlled by it are collectively called “MSC” herein.
FIG. 1 is a flowchart of initiating a call from a UE in the prior art. The MSC can convert the call request sent by the CS UE into a SIP Invite request. The conversion process includes the following steps.
Step S101: The calling CS UE sends a voice call request to the MSC through a setup message.
Step S102: The MSC performs protocol conversion for the voice call request of the calling CS UE, converts the CS domain setup message into a SIP Invite message, and sends the message to the called IMS UE through a Serving-Call Session Control Function (S-CSCF).
Step S103: The called IMS UE hooks off and answers the call, and returns a 200 OK message to the MSC.
Step S104: The MSC performs protocol conversion for the SIP 200 OK message, and converts the 200 OK message into a connect message. After receiving the connect message, the calling CS UE sets up a call with the called party.
The prior art has at least the following defects in the prior art. The MSC in the prior art supports only conversion between the 3GPP TS 24.008 and the SIP, for example, conversion from a Setup message into an Invite message, or conversion from an Invite message into a Setup message. Such signaling conversion implements only the basic functions such as setting up voice calls, and is unable to set up sophisticated services such as multimedia calls.